


Little Leak in the Lab

by FatePissOrder (poludeuces)



Category: Fate/Grand Order, Fate/stay night & Related Fandoms
Genre: If you don't like piss stuff don't read, Masturbation, Omorashi, Other, Piss, Watersports
Language: English
Status: Completed
Published: 2019-05-27
Updated: 2019-05-27
Packaged: 2020-03-20 02:40:36
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,877
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/18983545
Author URL: https://archiveofourown.org/users/poludeuces/pseuds/FatePissOrder
Summary: Paracelsus is the type to get completely caught up in his work, so that he doesn't realize how much he needs to go until it's too late.





	Little Leak in the Lab

**Author's Note:**

> hello. this is an omorashi/piss fanfic. if you do not like that, then i would recommend not reading this one  
> content warnings:  
> \- omorashi  
> \- pissing in a semi-public space (paracelsus' workshop)  
> \- description of pissing   
> \- character becoming turned on due to pissing  
> \- masturbation  
> \- ritsuka walks in after this has happened, but does not see the mess.
> 
> thanks!

“Make sure to remain hydrated,” Nightingale advises as she slams a glass of water onto Paracelsus’ desk. Normally, he would remind guests to his lab to be careful amongst the glass beakers and flasks filled with liquids only he knew the names of, but he knew that any attempt to negotiate with the berserker would lead to him being dragged off to the infirmary.

That was the reason for the tall glass of water. He had a tendency to lock himself up in his workshop, testing new mineralogy techniques that he could use. The new ruler, Astraea he believed her name to be, had arrived armed with interesting new gems he had never seen before. He had to hand over a large sum of his materials he had been saving up, and promise that whenever they were in battle together he would give her all of his buffs. Yet, these new gems were incredibly interesting, and as such, he had been spending even more time hidden away. That had led to Ritsuka popping his head in to check up on him, only to come face to face with a very dehydrated and almost-dead Paracelsus.

Nightingale had then been taking breaks from her time in the infirmary to pop by, always armed with a tall glass of water that she would slam onto his desk. He was tempted to tell her that if she wasn’t so rough with it, maybe a quarter of the glass wouldn’t spill onto the counter, but he didn’t want to push it too far.

“Thank you, Nightingale,” he thanks her, nodding to the glass to say that he has registered its existence. He returned to his work – Ritsuka had finally let him use some of the octuplet crystals in his experiments and he was extremely interested in what power they might hold. 

Normally, this is when she would leave, saying that she would be back in a couple of hours – and that she expected the glass to be finished.

Yet, this time, she stayed and crossed her arms.

Paracelsus looked up from his work to stare at her. It was often difficult for him to guess what she was thinking – he owed this up to her being a berserker. He straightened up his back so he was no longer bending over his crystals and pushed his bangs behind his ear. 

“Is there something wrong?” he asks. 

She nods to the glass of water, “Drink.”

He blinks in confusion, but takes the glass gingerly so as to not get the spilled water everywhere. He rubs the base of it with his hand so that it does not drip on his lap before putting the glass to his lips and taking a few, solid gulps. 

When he sets the glass down on his lap, Nightingale still does not look satisfied. “All of it.”

He smiles weakly, “All of it? I’ll drink all of it before you come back, I promise—”

“You told me that yesterday and you hadn’t,” Nightingale reminds him, and he blushes in response. 

To be honest, this was not the first glass he had been given that day. Ritsuka also seemed to be concerned with how many glasses of water he was drinking a day, and so he had downed a full glass for him. Never mind the cup of coffee Avicebron had gifted him that morning as they had their usual morning talk over breakfast.

This was all to say that he wasn’t sure if he’d be able to drink more without a break. 

And with the amount of work he wanted to get done that day, he did not want to take a break unless necessary. This conversation was already taking up too much of his time.  
However, even if he told all of this to the berserker, he was sure she wouldn’t take it as a valid excuse. 

“You must need to return to the infirmary now, I’m sure someone is in need of your services,” he tries. Nightingale was now the main doctor. If he could just get her to go back to her office, then he could return to his own studies, and then he could finish the glass of water at his own pace. One that wouldn’t make him need to burst soon.

She smiled. “BB is currently there – she told me I could take as long as I needed for my break.” 

It was then that Paracelsus knew that he was trapped. He would have to down this glass of water or he would never be able to resume his progress. Her smile reminded him of a teacher of his, way back when, or maybe the smile that Ritsuka would give him when he was going to be dragged into a full day of farming.

He sighed and lifted the glass back up. “You’re not going to leave until I do this.”

Nightingale nodded, “The health of all servants in Chaldea is a priority to me.”

Paracelsus swallowed thickly and looked down at the glass. He still had over half of the glass left to drink. Its contents swished around as he moved it up towards his lips. He couldn’t imagine drinking it fully – already his bladder was giving him tiny notices that maybe it was time to use the washroom. 

He gave one more sheepish glance up at Nightingale, who was still glaring at him intently, before bringing the glass up to his lips and taking three large gulps. He could feel his stomach groaning in response, suddenly feeling heavier. He took one hand from the glass to put his hand against it to hold back its protests. 

“Finish,” Nightingale said. Just under a quarter left remained in the glass. Withdrawing his hand from his belly, he threw his head back and finished the contents of the cup.   
With the same amount of gusto that Nightingale had used, he slammed the cup onto his desk. He smiled despite the pain. He felt very full suddenly, and the pressure from his bladder was much more noticeable now. 

She smiled and grabbed the cup. She walked over to one of his sinks and turned on the tap. The sudden gush of liquid from the faucet was tantalizing, and the sound of water filling up the cup deafening. Once it was filled up, she turned off the tap and returned the glass to his desk. He stared intently at the way the water sloshed around as it settled down. 

“Have that done when I come back in two hours,” Nightingale ordered. Before he could complain, she turned on her heel and walked out of his workshop.

Paracelsus sighed and brushed his bangs back before turning to his work once more. Despite the pressure now forming between his legs, he pushed that feeling down. He could do this. It wasn’t that long until when he would go for his late lunch, anyways. He had to make up some of that time he had wasted fulfilling Nightingale’s silly wish. If he was able to catch up, then he’d give himself that break.

He poured himself back into his work. The octuplet crystals were fascinating. He had been interested in how such a twinning pattern was possible, but studying them closely had certainly given new insights into how. He was also amazed by some of the tiny inclusions – perhaps he would make a thin section of it so he could look at it under the microscope. Paracelsus would have to see how many octuplet crystals Ritsuka had farmed up before potentially ruining a material though…

As he was about to run some of his mana into the crystal, a sudden pang of pressure pulled him out of his work. The pressure had returned. He glanced at the clock on the opposite of the room – it would have been almost an hour and a half since Nightingale had made him drink a full glass of water. He looked down at the crystal in his hands. He did not want to delay this any longer.

He crossed his legs and tried his best to ignore the pressure building.

Paracelsus returned his focus to his work. He breathed in and out, slowly letting the mana flow from his fingertips to the crystal.

Just like the flow from—

He shook his head, dispersing these thoughts. He had to concentrate! If anything went wrong, the crystal could break, and he was unsure if he could bring it back together as it had been originally. He was a master mineralogist, but he did not want to break something. Especially because of a silly thing like this. So he crossed his legs tighter.

He closed his eyes and instead focused on the glassy feeling of the mineral in his hands. Against his eyelids he could see his magic circuits buzzing with electricity. He had done something similar countless times before – what kind of caster would he be? – but anything could easily go wrong.

His fingertips cracked with mana, bright light dancing from his hands. He opened his eyes to study the dance. The way the power bounced enthralled him. He had seen this so many times before, but for some reason, this display had him open his mouth in interest. What would this material give him, if he gave just a little bit of power to it?

Unfortunately, putting all of his focus on the mineral had made him soften the tight grip of his crossed legs and he could feel a little piss escape.

He dropped the octuplet crystal immediately – thankfully it was not far – and shot a hand down to grab onto his cock. The sudden surprise had made the pee stop almost as quickly as it had began, but when he held on, he could definitely feel a small patch of dampness in his underwear.

With his other hand, Paracelsus lifted up the part of his jacket that covered his front to study the damage. Near his crotch, a small dark pool had started to spread, colouring his lap a slightly darker black than the rest of his pants. He gripped his penis harder, testing out the wetness. Thankfully, it was not too much. 

He relaxed on his stool. He squeezed his thighs while not relenting his grip on his dick. The sweet feeling of letting a little out was now overwhelming. Now that his body knew release, he would not be able to return to work without going to the washroom. Plus, he wouldn’t be able to use both of his hands.

So daintily, he stood up from his stool. He studied where he had been sitting – thankfully, none had spilled. He let his jacket fall as it would normally, but he squeezed his thighs to try to replace his hand. Paracelsus was not going to walk down the halls of Chaldea with his hand on his crotch. What if someone he respected saw him? Worse, what if a child saw him? He could almost hear Jack’s voice now, gleefully telling everyone about ‘Peeracelsus’.

It was not too far away from the closest bathrooms. He would need to walk up a flight of stairs, that would be the hardest part, but he should be alright if he left now.

He took one final glance at the full glass of water that Nightingale had left him, before exiting his workshop.

The walk to the washroom was hell. He tried his best to keep his head down, only nodding at some of his friends. He could almost see the look of worry that Jekyll gave him as Paracelsus assured him that he would be alright, yes, no, he didn’t need to be taken to the infirmary ( _anything_ but that—the nurse’s office was on the opposite end of Chaldea), he was fine, he just needed to be somewhere, and quick.

He just thanked his lucky stars that someone like Mephistopheles, who always seemed to be able to look through him, hadn’t been there to stop him. If the clown had showed up, Paracelsus was sure that he would have instantly known what was up, and done anything in his power to make sure Paracelsus would never reach the washroom.

He slowly made his way up the stairs. He wished he could just run up them, but every time he spread his legs just a little, the pressure doubled. His bladder was screaming at him by this point. He made sure to quickly squeeze his thighs together every time he cleared a step. 

He looked around him. He was half-way up. There was no one around, just a camera with its red recording light blinking at him. How likely was it that someone was watching him and his pain? Unlikely. Thus, he allowed himself to squeeze his dick, running the rest of the way up. The pressure felt heavenly, and it took him so much effort to remove his hand.

Once up the stairs, he could see the washrooms. He could only imagine his bladder cheering in response.

“Almost there,” he said to himself. He straightened his back and balled up his fists, half-walking and half-waddling to the washroom. Thankfully for him, the men’s was closer to where he was coming from. All he would need to do is hold up this act for a bit longer, and then he could rush to the urinals and fully spend himself.

This thought made him leak a little more, and he quickly shot his hand back down to stop himself. In this position, he would be unable to check the damage. He could only thank the gods that his jacket was hiding the wet patch. And he prayed that it did not seep into his white jacket.

He gripped his crotch and gave a testing squeeze. His underwear was now uncomfortably sticky. And the patch had spread out to his front, so his thighs felt cool from the wetness. He would likely need to go back to his room – take a shower, throw on some new clothes and discreetly throw these ones in the wash. Maybe he could spill some chemicals on other ones and that would hide the stench.

The image of a shower and then a washing machine made his bladder pang again. Oh, how lovely it would be to pee in the shower right now – no requirement to hold his dick, just letting his stream go where it pleased, marking whatever it wanted to…

He shook these thoughts from his mind and briskly walked to the door. He violently yanked on the door, only for it not to open. 

Oh no.

He tried a couple more yanks, before looking at the door. It was only then that he saw the sign: 

_Bathroom closed due to_ some _servants fighting._

Never before did he swear so much in his head. Truly, being in Chaldea with a bunch of brutes was hell.

Leaning against the door with his hand on his crotch, he wracked his brain for possible answers. The closest bathroom to this was in the dorms, but that was much too far away. He could try to run to the one closer to the dinning hall, but that meant more people would see him in this state. The possible embarrassment of people commenting would be too much to bear.

He sighed. The best course of action would be to return to his quiet workshop. There, he could find a possible receptacle. 

With this goal set in his mind, he did not care who saw him as he bolted down the stairs and back to his workshop.

He locked the door and, hand on his dick, made his way into the room. Where could he go? There was the sink, but he wasn’t confident on climbing up onto the counter in this state. Plus, he was better than that.

There were some beakers, but they were much too small for the amount of piss he needed to let out. He could empty the glass Nightingale brought, but even that would likely spill over.

His eyes landed on a large Erlenmeyer flask. That should work. He rushed over and grabbed it, popping off the cork with his thumb. He made his way to his stool. Paracelsus wasn’t sure if he’d be able to stand up and go, with how much his legs were shaking.

He sat down, and awkwardly fished his dick out of his pants. The sudden air on the head of his penis triggered his body’s natural reflex, and piss stared to flow out. He tried his best to calm it, but the sweet feeling of release was too much. He successfully got it to only dribble out, as he pointed the stream towards the lip of the flask.

“There,” he panted. He then allowed himself to go. 

The stream was strong, gushing out like a hose. It hit the side of the flask before dribbling down to the bottom. It resembled a waterfall, he remarked, watching the yellow cascade down the side. 

He readjusted his hold on the flask before closing his eyes and releasing the breath he hadn’t known he was holding until then. With his eyes closed, he was able to focus on the feeling of peeing, how it escaped his body and the strong sound of his hose emptying. He threw his head back and smiled faintly. 

Soon, the flask started to fill with his piss, feeling heavier in his hand. He opened his eyes, watching as the yellow liquid gushed into the container. As it was a flask, he could see as it passed each volume line, telling him how much he had spent.

Yet, it was perhaps filling up _too fast._

“Oh no.” He fumbled to grab onto his dick. Now that he had been able to go, his body was not happy to suddenly stop. But if he didn’t it would quickly spill over and he would have a larger mess on his hands. He squeezed down hard, so that only dribbles escaped, as he tried to find a new receptacle for the rest of his bladder’s contents.

The problem was that because he was sitting on his stool, he would need to stand up if he wanted to grab something. Nothing was in arm’s reach. He could feel his bladder protesting, and he was dribbling still. If he got up, he was unsure what would happen. 

He looked back down at his lap. The wet patch had traveled down one thigh, before thinning out as it reached his boots. His toes were a little wet now because of it. His underwear was ruined, now dyed yellow. He almost smiled at it – he had successfully marked himself. 

In front of him, the dribbles had hit a cupboard – if he recalled correctly, he kept the burners in there. The piss had stained the cupboards a darker brown colour, and they traveled down to form a small puddle of his piss at the base. It dripped down tantalizingly from the bottom lip of the cupboard to the floor. 

Paracelsus bit his lip. He would already have to clean it up, anyways. How much worse would it be if he just peed the rest of it, here?

He had made up his mind and moved his hand, letting his dick fall between his legs. He spread his legs and allowed the stream to continue full blast.

He watched the way it hit the cupboard, flying off from the sheer force of his hose. It was getting a strong watering, and he smiled, watching as his piss made it even darker in colour. His eyes fluttered down to the pool at the base, and he had to bite his lip further – this was his creation, and he smiled at the way it grew.

“You already filled up a flask but that wasn’t enough, huh?” he told himself, grabbing his dick and now pointing it down to the floor. 

The stream was slowing down as his bladder spent itself. It was now much easier to control, and he tried his best to add to his little lake and not to his clothes. 

Finally, the little dribbles were all that was left, and he let them drop down and join their friends on the floor. He pushed the stool back so he could admire his handiwork. His dick jolted in his hand as a blush decorated his cheeks – he was embarrassed by how much this had started to turn him on.

He swallowed and started working his hand up and down on his dick, his urine partially working as lubricant. The smell of ammonia and piss wafted up to his nostrils, completely drowning the usual chemical smell from his lab. It made him increase his pace, spreading his legs and putting his feet up on the bottom rung of his stool, his eyes darting between his handiwork and his erect penis.

He pressed down on the head, tightening his grip similarly to how he had when holding. This was enough – he orgasmed soon after, his come joining his piss on the floor. 

Paracelsus panted, watching the mess he had made settle. There was now a sizeable lake of his own piss on the floor, mixing with his come, while the cupboards still dripped any remaining piss. On the counter, gleaming under the lights, was the giant flask, filled to the brim. He licked his lips and let out a shaky laugh.

Despite the embarrassment of it all, he could not deny how amazing it had all felt.

“Paracelsus!”

His thoughts were cut as he saw his master walk through the door. He had forgotten that Ritsuka was able to go anywhere he pleased. Thankfully, he had used the door to the opposite side. With the heights of the countertops, it was unlikely that he could see his servant’s current state – legs spread, dick out, and a puddle of piss on the floor.

Or if he could, he said nothing about it.

“Y-yes, master?” Paracelsus asked, licking his lips. He hadn’t realized how dry his mouth was until that moment.

“Is everything alright? Some people saw you running around and Nightingale got caught up because Li Shuwen broke his head or something and asked me to come around and see if you had finished your water yet.”

“I am fine!” Paracelsus said, “That is another glass I filled up for myself.” He nodded to the full glass. If Ritsuka thought he was lying, he said nothing about it.

Rather, he scrunched up his nose and covered his face with his hand. “Ew gross, what’s that smell?”

Paracelsus smiled faintly – so he could smell it, huh? He quickly wiped it from his face. “I’m working with an ammonia solution, don’t worry.”

Ritsuka nodded and waved his hand. “Okay, just, make sure to stay hydrated, alright?” He quickly exited the lab, leaving Paracelsus.

He smiled and slowly got up from his stool, making sure not to step on his mess. He placed his dick back in his underwear, savouring the wetness against his hand.

At that moment, his mind caught up to his actions, and he blushed hard. “God,” he said to himself, before quickly making work of his mess.

Next time, he would listen to his bladder.

**Author's Note:**

> hello! thanks for reading!  
> i've become more confident with nsfw stuff recently, so i have started to dabble more in my kinks, omo and piss being a big one for me. i hope that there are some fans in the fgo community.  
> paracelsus has always been a favourite of mine, and his design is so good.  
> again thank you for reading! i'm planning on doing more piss fics for fgo, so let me know if there's other characters you can see with omo/piss and maybe i'll write it!


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